Seven healthy volunteers (four males, 20-28 years) were studied to determine the effect of parenteral nutrition (PN) on ampicillin clearance. Each volunteer received intravenous infusions of 1 liter of PN (3.75% amino acid and 10% dextrose) alternating with 1 liter of 10% dextrose (containing all additives as PN except for calcium and phosphorus); and a meal containing similar fluid volume, caloric, protein, and sodium content as the PN solution. Ampicillin (250 mg) was given intravenously 2 hr after commencement of each intravenous solution and 4 hr after the meal. During PN infusion, the mean (+/- SE) glomerular filtration rate (GFR) as indicated by creatinine clearance was 125 +/- 18 ml/min; ampicillin pharmacokinetic data included area under the serum ampicillin concentration-time curve of 899 +/- 118 micrograms min/ml, terminal elimination half life of 37 +/- 4.3 min, volume of distribution at steady state of 11.9 +/- 1.6 liter, total body clearance of 4.7 +/- 0.6 ml/min/kg, renal clearance of 3.8 +/- 0.5 ml/min/kg, and 82 +/- 6.7% of the ampicillin administered was excreted in urine over 10 hr. The results were not significantly altered by different nutrient regimens or the order of infusion of intravenous solutions. We conclude that the use of PN is unlikely to affect the pharmacokinetics of ampicillin provided the renal functions including GFR, remain unchanged.